Method and system for regenerating a gasoline particulate filter

ABSTRACT

Methods and systems are presented for regenerating a particulate filter. In one example, vehicle speed control mode parameters may be adjusted in response to an amount of soot stored in a particulate filter being greater than a first threshold. The vehicle speed control parameters may be returned to base values in response to the amount of soot stored in the particulate filter being less than a second threshold.

CROSS REFERENCE TO RELATED APPLICATION

The present application is a continuation of U.S. Patent Application No.14/958,277, entitled “METHOD AND SYSTEM FOR REGENERATING A GASOLINEPARTICULATE FILTER,” filed on Dec. 3, 2015. The entire contents of theabove-referenced application are hereby incorporated by reference in itsentirety for all purposes.

FIELD

The present description relates generally to methods and systems forimproving the possibility for regenerating a gasoline particulate filter(GPF) while a vehicle is operating in an automatic speed control mode.

BACKGROUND/SUMMARY

A vehicle that includes a direct injection gasoline engine may include aGPF. The GPF may store carbonaceous soot produced by the directinjection engine. From time to time, the GPF may be regenerated toreduce exhaust back pressure and the amount of soot stored in the GPF.The GPF may be regenerated by operating the GPF above a thresholdtemperature and providing excess oxygen to the GPF. The excess oxygenmay help to combust soot stored in the GPF, thereby reducing the amountof soot stored in the GPF. The excess oxygen may be provided bycombusting a lean air-fuel ratio in the engine or via providing air tothe GPF. However, vehicle emissions may increase if the engine isoperated with a lean air-fuel ratio or if air is provided to thevehicle's exhaust gas after treatment system. Therefore, it may bedesirable to increase the possibility of operating the vehicle duringconditions where oxygen may be provided to the GPF without increasingvehicle emissions.

The inventors herein have recognized the above-mentioned issue and havedeveloped a vehicle system, comprising: a spark ignited engine; anexhaust system coupled to the spark ignited engine, the exhaust systemincluding a particulate filter; and a controller, the controllerincluding executable instructions stored in non-transitory memory tooperate the spark ignited engine and adjust one or more automaticvehicle speed controller parameters in response to an amount of sootstored in a particulate filter greater than a threshold amount.

By adjusting one or more vehicle speed controller parameters in responseto an amount of soot stored in a particulate filter, it may be possibleto provide the technical result of regenerating a particulate filtermore frequently than if the vehicle operates with a same group ofvehicle speed controller parameters during automatic vehicle speedcontrol. In particular, base vehicle speed controller control limits maybe populated with values that maintain vehicle speed at a desiredvehicle speed plus or minus a predetermined vehicle speed. Further, thevehicle speed controller may include modest gains to maintain vehiclespeed within an upper vehicle speed limit and a lower vehicle speedlimit. However, if a large amount of soot is stored in the particulatefilter, the vehicle speed controller gains may be increased and thedesired vehicle speed range may be increased to induce more frequententry into deceleration fuel shut-off so that the particulate filter maybe passively regenerated while operating the vehicle in a speed controlmode.

For example, when an amount of soot stored in a particulate filter isless than a first threshold, a desired vehicle speed may be 100 KPH. Thecontroller may have an upper vehicle speed boundary of 103 KPH and alower vehicle speed boundary of 97 KPH. If vehicle speed exceeds 103KPH, engine torque may be gradually reduced so as to not make rapidengine torque changes. Similarly, if vehicle speed is less than 97 KPH,engine torque may be gradually increased so as to provide a gradualincrease in engine torque and vehicle speed. In this way, vehicle speedmay be controlled to desired vehicle speed without inducing largerengine torque changes when the amount of soot stored in a particulatefilter is less than a first threshold.

On the other hand, if the amount of soot stored in the particulatefilter is greater than a threshold, vehicle speed controller parametersmay be adjusted to increase the possibility of entering a decelerationfuel shut-off mode. For example, the controller upper vehicle speedlimit may be adjusted to 108 KPH and a lower vehicle speed limit may beadjusted to 93 KPH for a desired vehicle speed of 100 KPH. Further, thevehicle speed controller gains may be made more aggressive (e.g.,increased) in response to the amount of soot stored within theparticulate filter.

The vehicle speed control upper vehicle speed limit may be increased anda lower vehicle speed limit may be decreased in response to the amountof soot stored in the particulate filter being greater than a thresholdto allow requested engine torque to approach zero for a longer period oftime if the vehicle encounters a negative grade. Further, the vehiclespeed controller gains may be increased in response to the amount ofsoot stored in the particulate filter being greater than the thresholdso that larger and longer engine torque reductions may be provided toincrease the possibility of entering deceleration fuel shut-off mode.

The present description may provide several advantages. In particular,the approach may increase the propensity for larger engine torquechanges while operating a vehicle in an automatic speed control mode sothat the vehicle has a greater possibility of entering deceleration fuelshut-off mode. Further, the approach may reduce the possibility of theparticulate filter being actively regenerated, thereby increasingvehicle fuel efficiency. Further still, the approach may increase thepossibility of the particulate filter being ready for regenerationduring a deceleration fuel shut-off mode.

The above advantages and other advantages, and features of the presentdescription will be readily apparent from the following DetailedDescription when taken alone or in connection with the accompanyingdrawings.

It should be understood that the summary above is provided to introducein simplified form a selection of concepts that are further described inthe detailed description. It is not meant to identify key or essentialfeatures of the claimed subject matter, the scope of which is defineduniquely by the claims that follow the detailed description.Furthermore, the claimed subject matter is not limited toimplementations that solve any disadvantages noted above or in any partof this disclosure.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 shows an example vehicle that may be included in the systems andmethods described herein;

FIG. 2 shows an example engine for the vehicle of FIG. 1;

FIG. 3 shows an example powertrain for the vehicle of FIG. 1;

FIG. 4 shows a block diagram of an example vehicle speed controller;

FIG. 5 shows an example method for operating a vehicle; and

FIG. 6 shows an example vehicle operating sequence according to themethod of FIG. 5.

DETAILED DESCRIPTION

The following description relates to systems and methods forregenerating a particulate filter while a vehicle is operating in anautomatic speed or cruise control mode. FIG. 1 shows a non-limitingexample vehicle for operating in a cruise control mode and passivelyregenerating a particulate filter. FIG. 2 shows an example engine forthe vehicle of FIG. 1. A powertrain or driveline for the vehicle of FIG.1 is shown in FIG. 3. A block diagram for an example vehicle speedcontroller is shown in FIG. 4. A method of operating a vehicle is shownin FIG. 5. Finally, a vehicle operating sequence according to the methodof FIG. 5 is shown in FIG. 6.

Referring now to FIG. 1, vehicle 100 includes a controller 12 forreceiving sensor data and adjusting actuators. Controller 12 may operatevehicle 100 in a cruise control mode where vehicle speed is maintainedwithin a desired vehicle speed range bounded by upper and lower vehiclespeed thresholds. In some examples, controller 12 may cooperate withadditional controllers to operate vehicle 100. Vehicle 100 is shown withglobal positioning system (GPS) receiver 130. Satellite 102 providestime stamped information to GPS receiver 130 which relays theinformation to vehicle position determining system 140. Vehiclepositioning determination system 140 relays present and future roadgrade data to controller 12 based on Satellite data. Vehicle 100 mayalso be equipped with optional camera 135 for surveying road conditionsin the path of vehicle 135. For example, camera 135 may acquire roadconditions from road side signs 166 or displays. Vehicle positiondetermining system 140 may alternatively acquire information fordetermining vehicle position from stationary broadcast tower 104 viareceiver 132. In some examples, vehicle 100 may also include a sensor138 for determining the proximity of vehicles in the travel path ofvehicle 100. Sensor 138 may be laser, sound, or radar signal based.

In this example, vehicle 100 is shown as a passenger vehicle. However,in some examples, vehicle 100 may be a commercial vehicle such as afreight hauling semi-trailer or a truck.

Referring now to FIG. 2, an example vehicle engine is shown. In thisexample, the engine is a spark ignition engine (e.g., combustion in theengine is initiated via a spark produced via a spark plug).

FIG. 2 is schematic diagram showing one cylinder of a multi-cylinderengine 230 in an engine system 200 is shown. Engine 230 may becontrolled at least partially by a control system including a controller12 and by input from a vehicle operator 282 via an input device 280. Inthis example, the input device 280 includes an accelerator pedal and apedal position sensor 284 for generating a proportional pedal positionsignal.

A combustion chamber 232 of the engine 230 may include a cylinder formedby cylinder walls 234 with a piston 236 positioned therein. The piston236 may be coupled to a crankshaft 240 so that reciprocating motion ofthe piston is translated into rotational motion of the crankshaft. Thecrankshaft 240 may be coupled to at least one drive wheel of a vehiclevia an intermediate transmission system. Further, a starter motor may becoupled to the crankshaft 240 via a flywheel to enable a startingoperation of the engine 230.

Combustion chamber 232 may receive intake air from an intake manifold244 via an intake passage 242 and may exhaust combustion gases via anexhaust passage 248. The intake manifold 344 and the exhaust passage 248can selectively communicate with the combustion chamber 232 viarespective intake valve 252 and exhaust valve 254. In some examples, thecombustion chamber 232 may include two or more intake valves and/or twoor more exhaust valves.

In this example, the intake valve 252 and exhaust valve 254 may becontrolled by cam actuation via respective cam actuation systems 251 and253. The cam actuation systems 251 and 253 may each include one or morecams and may utilize one or more of cam profile switching (CPS),variable cam timing (VCT), variable valve timing (VVT), and/or variablevalve lift (VVL) systems that may be operated by the controller 12 tovary valve operation. The position of the intake valve 252 and exhaustvalve 254 may be determined by position sensors 255 and 257,respectively. In alternative examples, the intake valve 252 and/orexhaust valve 254 may be controlled by electric valve actuation. Forexample, the cylinder 232 may alternatively include an intake valvecontrolled via electric valve actuation and an exhaust valve controlledvia cam actuation including CPS and/or VCT systems.

A fuel injector 269 is shown coupled directly to combustion chamber 232for injecting fuel directly therein in proportion to the pulse width ofa signal received from the controller 12. In this manner, the fuelinjector 269 provides what is known as direct injection of fuel into thecombustion chamber 232. The fuel injector may be mounted in the side ofthe combustion chamber or in the top of the combustion chamber, forexample. Fuel may be delivered to the fuel injector 269 by a fuel system(not shown) including a fuel tank, a fuel pump, and a fuel rail. In someexamples, the combustion chamber 232 may alternatively or additionallyinclude a fuel injector arranged in the intake manifold 244 in aconfiguration that provides what is known as port injection of fuel intothe intake port upstream of the combustion chamber 232.

Spark is provided to combustion chamber 232 via spark plug 266. Theignition system may further comprise an ignition coil (not shown) forincreasing voltage supplied to spark plug 266.

The intake passage 242 may include a throttle 262 having a throttleplate 264. In this particular example, the position of throttle plate264 may be varied by the controller 12 via a signal provided to anelectric motor or actuator included with the throttle 262, aconfiguration that is commonly referred to as electronic throttlecontrol (ETC). In this manner, the throttle 262 may be operated to varythe intake air provided to the combustion chamber 232 among other enginecylinders. The position of the throttle plate 264 may be provided to thecontroller 12 by a throttle position signal. The intake passage 242 mayinclude a mass air flow sensor 220 and a manifold air pressure sensor222 for sensing an amount of air entering engine 230.

An exhaust gas sensor 227 is shown coupled to the exhaust passage 248upstream of an emission control device 270 according to a direction ofexhaust flow. The sensor 227 may be any suitable sensor for providing anindication of exhaust gas air-fuel ratio such as a linear oxygen sensoror UEGO (universal or wide-range exhaust gas oxygen), a two-state oxygensensor or EGO, a HEGO (heated EGO), a NO_(x), HC, or CO sensor. In oneexample, upstream exhaust gas sensor 227 is a UEGO configured to provideoutput, such as a voltage signal, that is proportional to the amount ofoxygen present in the exhaust. Controller 12 converts oxygen sensoroutput into exhaust gas air-fuel ratio via an oxygen sensor transferfunction.

The emission control device 270 is shown arranged along the exhaustpassage 248 downstream of the exhaust gas sensor 227. The device 270 maybe a three way catalyst (TWC), NO_(x) trap, a particulate filter, orcombinations thereof. In some examples, during operation of the engine230, the emission control device 270 may be periodically reset byoperating at least one cylinder of the engine within a particularair-fuel ratio. In examples where emissions control device 270 is aparticulate filter, soot trapped in emissions control device 270 may becombusted to regenerate the device. A pressure ratio across emissionscontrol device 270 may be determined from pressure sensors 277 and 278.The pressure ratio may be indicative of an amount of soot stored in theemissions control device 270.

The controller 12 is shown in FIG. 3 as a microcomputer, including amicroprocessor unit 202, input/output ports 204, an electronic storagemedium for executable programs and calibration values shown as read onlymemory chip 206 (e.g., non-transitory memory) in this particularexample, random access memory 208, keep alive memory 210, and a databus. The controller 12 may receive various signals from sensors coupledto the engine 230, in addition to those signals previously discussed,including measurement of inducted mass air flow (MAF) from the mass airflow sensor 220; engine coolant temperature (ECT) from a temperaturesensor 223 coupled to a cooling sleeve 214; an engine position signalfrom a Hall effect sensor 218 (or other type) sensing a position ofcrankshaft 240; throttle position from a throttle position sensor 265;and manifold absolute pressure (MAP) signal from the sensor 222. Anengine speed signal may be generated by the controller 12 fromcrankshaft position sensor 218. Manifold pressure signal also providesan indication of vacuum, or pressure, in the intake manifold 244. Notethat various combinations of the above sensors may be used, such as aMAF sensor without a MAP sensor, or vice versa. During engine operation,engine torque may be inferred from the output of MAP sensor 222 andengine speed. Further, this sensor, along with the detected enginespeed, may be a basis for estimating charge (including air) inductedinto the cylinder. In one example, the crankshaft position sensor 218,which is also used as an engine speed sensor, may produce apredetermined number of equally spaced pulses every revolution of thecrankshaft.

The storage medium read-only memory 206 can be programmed with computerreadable data representing non-transitory instructions executable by theprocessor 202 for performing at least portions of the methods describedbelow as well as other variants that are anticipated but notspecifically listed.

During operation, each cylinder within engine 230 typically undergoes afour stroke cycle: the cycle includes the intake stroke, compressionstroke, expansion stroke, and exhaust stroke. During the intake stroke,generally, the exhaust valve 254 closes and intake valve 252 opens. Airis introduced into combustion chamber 232 via intake manifold 244, andpiston 236 moves to the bottom of the cylinder so as to increase thevolume within combustion chamber 232. The position at which piston 236is near the bottom of the cylinder and at the end of its stroke (e.g.,when combustion chamber 232 is at its largest volume) is typicallyreferred to by those of skill in the art as bottom dead center (BDC).

During the compression stroke, intake valve 252 and exhaust valve 254are closed. Piston 236 moves toward the cylinder head so as to compressthe air within combustion chamber 232. The point at which piston 236 isat the end of its stroke and closest to the cylinder head (e.g., whencombustion chamber 232 is at its smallest volume) is typically referredto by those of skill in the art as top dead center (TDC). In a processhereinafter referred to as injection, fuel is introduced into thecombustion chamber. In a process hereinafter referred to as ignition,the injected fuel is ignited by known ignition means such as spark plug266, resulting in combustion.

During the expansion stroke, the expanding gases push piston 236 back toBDC. Crankshaft 240 converts piston movement into a rotational torque ofthe rotary shaft. Finally, during the exhaust stroke, the exhaust valve254 opens to release the combusted air-fuel mixture to exhaust manifold248 and the piston returns to TDC. Note that the above is shown merelyas an example, and that intake and exhaust valve opening and/or closingtimings may vary, such as to provide positive or negative valve overlap,late intake valve closing, or various other examples.

As described above, FIG. 2 shows only one cylinder of a multi-cylinderengine, and each cylinder may similarly include its own set ofintake/exhaust valves, fuel injector, spark plug, etc.

Referring now to FIG. 3, a schematic of a vehicle drive-train 300 isshown. Drive-train 300 may be powered by engine 230 as shown in greaterdetail in FIG. 2. In one example, engine 230 may be a gasoline engine.Engine 230 may be started with an engine starting system (not shown).Further, engine 230 may generate or adjust torque via torque actuator304, such as a fuel injector, throttle, cam, etc.

An engine output torque may be transmitted to torque converter 306 todrive a step-ratio automatic transmission 308 by engaging one or moreclutches, including forward clutch 310, where the torque converter maybe referred to as a component of the transmission. Torque converter 306includes an impeller 320 that transmits torque to turbine 322 viahydraulic fluid. One or more gear clutches 324 may be engaged to changegear ratios between engine 230 and vehicle wheels 314. The output of thetorque converter 306 may in turn be controlled by torque converterlock-up clutch 312. As such, when torque converter lock-up clutch 312 isfully disengaged, torque converter 306 transmits torque to automatictransmission 308 via fluid transfer between the torque converter turbine322 and torque converter impeller 320, thereby enabling torquemultiplication. In contrast, when torque converter lock-up clutch 312 isfully engaged, the engine output torque is directly transferred via thetorque converter clutch 312 to an input shaft of transmission 308.Alternatively, the torque converter lock-up clutch 312 may be partiallyengaged, thereby enabling the amount of torque relayed to thetransmission to be adjusted. A controller 12 may be configured to adjustthe amount of torque transmitted by the torque converter by adjustingthe torque converter lock-up clutch in response to various engineoperating conditions, or based on a driver-based engine operationrequest.

Torque output from the automatic transmission 308 may in turn be relayedto wheels 314 to propel the vehicle. Specifically, automatictransmission 308 may adjust an input driving torque at the input shaft(not shown) responsive to a vehicle traveling condition beforetransmitting an output driving torque to the wheels. Vehicle speed maybe determined via speed sensor 330.

Further, wheels 314 may be locked by engaging wheel brakes 316. In oneexample, wheel brakes 316 may be engaged in response to the driverpressing his foot on a brake pedal (not shown). In the similar way,wheels 314 may be unlocked by disengaging wheel brakes 316 in responseto the driver releasing his foot from the brake pedal.

Referring now to FIG. 4, a block diagram of an example vehicle cruisecontrol system is shown. Vehicle speed control system or cruise controlsystem 400 includes a desired vehicle speed. The desired vehicle speedmay be input via a driver or it may be the vehicle's present speed whena driver activates speed control mode via a switch or other input. Thedesired vehicle speed is input to summing junction 404 and block 406.

System 408 estimates an amount of soot stored in the vehicle'sparticulate filter at 408. In one example, the amount of soot isestimated based on air flow through the engine and a pressure dropacross the particulate filter at the present engine air flow rate. Inone example, a table or function holds empirically determined sootamounts. The table or function is indexed via engine air flow rate andthe pressure drop across the particulate filter. The soot amountdetermined at 408 is input to block 406 and block 410.

At block 406, the soot load estimate and desired vehicle speed are abasis for determining the vehicle upper and lower speed limits foroperating in speed control mode. In one example, the soot load estimateis used to index a function that outputs adder values that are a basisfor the vehicle's upper speed limit and the vehicle's lower speed limit.In particular, the adder values are added to the desired vehicle speeddetermined at 402. For example, if the function outputs a value of 3KPH, the desired vehicle speed determined at 402 plus 3 KPH equals thevehicle's upper speed limit. The desired vehicle speed minus 3 KPHequals the vehicle's lower speed limit. The upper and lower vehiclespeed limits are input to block 410.

At 404, actual vehicle speed determined from transmission 308 issubtracted from desired vehicle speed to produce a vehicle speed error.The vehicle speed error is passed to block 410.

At block 410, the vehicle speed error is multiplied by a proportionalgain value. The proportional gain value is output from one or moretables or functions that are selected based on the vehicle speedrelative to the vehicle upper speed limit and the vehicle lower speedlimit. The proportional gain is further based on the amount of sootstored in the particulate filter. In one example, the proportional gainis output from one of six tables or functions. A first table suppliesthe proportional gain when vehicle speed is less than the lower vehiclespeed limit when the amount of soot stored in the particulate filter isgreater than a threshold or when particulate filter regeneration isbeing called for (e.g., when SOOT_MAX_LATCH equals 1). A second tablesupplies the proportional gain when vehicle speed is less than the lowervehicle speed limit when the amount of soot stored in the particulatefilter is less than a threshold or when particulate filter regenerationis not being called for (e.g., when SOOT_MAX_LATCH equals 0). A thirdtable supplies the proportional gain when vehicle speed is greater thanthe lower vehicle speed limit and less than the upper vehicle speedlimit when the amount of soot stored in the particulate filter isgreater than a threshold or when particulate filter regeneration isbeing called for (e.g., when SOOT_MAX_LATCH equals 1). A fourth tablesupplies the proportional gain when vehicle speed is greater than thelower vehicle speed limit and less than the upper vehicle speed limitwhen the amount of soot stored in the particulate filter is less than athreshold or when particulate filter regeneration is being called for(e.g., when SOOT_MAX_LATCH equals 0). A fifth table supplies theproportional gain when vehicle speed is greater than the upper vehiclespeed limit when the amount of soot stored in the particulate filter isgreater than a threshold or when particulate filter regeneration isbeing called for (e.g., when SOOT_MAX_LATCH equals 1). A sixth tablesupplies the proportional gain when vehicle speed is greater than theupper vehicle speed limit when the amount of soot stored in theparticulate filter is less than a threshold or when particulate filterregeneration is being called for (e.g., when SOOT_MAX_LATCH equals 0).The result of the multiplication is passed to block 412.

At block 412, controller 400 adjusts one or more engine actuators (e.g.,throttle, fuel injection timing, etc.) to increase or decrease enginetorque to that vehicle speed may be regulated toward the desired vehiclespeed. The engine torque adjustments are applied to the engine 230. Theengine torque is applied to transmission 308 to adjust vehicle speed.

It should be noted that controller 400 is exemplary in nature and is notintended to be limiting. For example, the desired vehicle speed andamount of soot stored in the particulate filter may be a basis foradjusting proportional and integral gains in a proportional/integralvehicle speed controller. Further, the desired vehicle speed and amountof soot stored in the particulate filter may be a basis for adjustingvalues in a gain matrix of a state-space controller or other knowncontroller types. Further, upper and lower vehicle speed limits invarious possible controller designs may be adjusted based on the desiredvehicle speed and the amount of soot stored in the particulate filter.The gains and limits may be empirically determined and stored incontroller memory.

Thus, the system of FIGS. 1-4 provides for a vehicle system, comprising:a spark ignited engine; an exhaust system coupled to the spark ignitedengine, the exhaust system including a particulate filter; and acontroller, the controller including executable instructions stored innon-transitory memory to operate the spark ignited engine and adjust oneor more automatic vehicle speed controller parameters in response to anamount of soot stored in a particulate filter greater than a thresholdamount. The vehicle system further comprises additional instructions tocontrol an amount of air flowing through the spark ignited engine duringa condition of deceleration fuel shut-off in response to the amount ofsoot stored in the particulate filter.

In some examples, the vehicle system further comprises additionalinstructions to retard spark timing of the spark ignited engine inresponse to being a within a threshold distance of an expected roadcondition where deceleration fuel shut off is expected. The vehiclesystem includes where the one or more automatic vehicle speed controllerparameters includes a controller gain variable. The vehicle systemincludes where the one or more automatic vehicle speed controllerparameters includes a controller upper vehicle speed limit. The vehiclesystem includes where the one or more automatic vehicle speed controllerparameters are adjusted to increase the possibility of entering adeceleration fuel shut-off mode of operation. The vehicle systemincludes where fuel supplied to one or more engine cylinders ceases toflow in the deceleration fuel shut-off mode.

The system of FIGS. 1-4 also provides for a vehicle system, comprising:a spark ignited engine; a controller, the controller includingexecutable instructions stored in non-transitory memory to operate thespark ignited engine and enter a deceleration fuel shut-off mode inresponse to vehicle conditions resulting from road conditions of asection of road and an amount of soot stored in a particulate filterbeing greater than a threshold amount while the vehicle is operated in aspeed control mode. The vehicle system further comprises additionalinstructions to not enter the deceleration fuel shut-off mode inresponse to vehicle conditions resulting from road conditions of thesection of road and the amount of soot stored in the particulate filterbeing less than the threshold amount while the vehicle is operating inthe speed control mode.

In some examples, the vehicle system further comprises adjusting one ormore vehicle speed control parameters in response to the amount of sootstored in the particulate filter being greater than the thresholdamount. The vehicle system includes where the road condition is a changein road grade. The vehicle system includes where the change in roadgrade is from a positive grade to a negative grade. The vehicle systemfurther comprises additional instructions to retard spark timing inanticipation of a road condition and the amount of soot stored in theparticulate filter being greater than the threshold amount. The vehiclesystem includes where the road condition is anticipated via a navigationsystem.

Referring now to FIG. 5, an example method 500 for operating a vehiclewith a particulate filter is shown. At least portions of method 500 maybe included in a system as shown in FIGS. 1-3 as executable instructionsstored in non-transitory memory. Further, portions of method 500 may beperformed in the physical world via a controller, actuators, andsensors. Additionally, the method of FIG. 5 may provide the operatingsequence shown in FIG. 6. The methods of FIG. 5 may be performedreal-time in a vehicle driving on a road.

At 502, method 500 judges if vehicle cruise control mode is requested.Vehicle cruise control may be requested via a driver operating a pushbutton or other human/machine interface. In vehicle speed control modeor cruise control mode, vehicle speed is controlled to a desired speedrequest by the driver. Engine torque is adjusted via a torque actuatorsuch as a throttle, fuel injectors, and/or cam timing to control vehiclespeed to the desired speed. Thus, engine torque may be varied oradjusted to maintain vehicle speed at the desired vehicle speedrequested by the driver. Method 500 proceeds to 504 if vehicle speedcontrol mode is requested. Otherwise, method 500 exits.

At 504, method 500 judges GPF soot load (e.g., amount of soot stored inthe particulate filter) is greater than (G.T.) a first threshold or if avariable in controller memory SOOT_MAX_LATCH is set to a predeterminedvalue (e.g., 1). If so, method 500 proceeds to 508. Otherwise, method500 proceeds to 506. Setting SOOT_MAX_LATCH enables passive regenerationof the particulate filter to occur while the vehicle is moving and isbeing driven.

At 506, method 500 monitors one or more sensors to estimate the amountof soot stored in the particulate filter. In one example, the amount ofsoot stored in the particulate filter may be estimated based on apressure ratio across the particulate filter while the engine iscombusting air and fuel. The pressure ratio indexes a table or functionthat contains empirically determined amounts of soot stored in theparticulate filter based on a pressure ratio across the particulatefilter. Method 500 proceeds to 507 after the amount of soot stored inthe particulate filter is determined.

At 507, method 500 adjusts vehicle speed controller gains and limits tobase values (e.g., values used when particulate matter stored within theparticulate filter is less than a second threshold). The base values mayconstrain the vehicle speed upper and lower limits closer to the desiredvehicle speed than the vehicle speed upper and lower limits when theparticulate filter is storing more than a first threshold amount ofsoot. For example, a base upper vehicle speed limit may be 104 KPH whendesired vehicle speed is 100 KPH and an upper vehicle speed limit whenthe particulate filter is storing more than a first threshold amount ofsoot may be 107 KPH when the desired vehicle speed is 100 KPH. A baselower vehicle speed limit may be 96 KPH when desired vehicle speed is100 KPH and a lower vehicle speed limit when the particulate filter isstoring more than a first threshold amount of soot may be 93 KPH whenthe desired vehicle speed is 100 KPH. Further, vehicle speed controllergains may be returned to base values for times when the amount of sootstored in the particulate filter is less than the second thresholdamount. In one example, the base vehicle speed controller gains for whenthe amount of soot stored in the particulate filter is less than thesecond threshold may be decreased as compared to vehicle speedcontroller gains when the amount of soot stored in the particulatefilter is greater than the first threshold. Consequently, engine torquedemands may not change as quick when the amount of soot stored in theparticulate filter is less than the second threshold so as not to enterdeceleration fuel shut-off frequently. Method 500 returns to 502 aftervehicle speed controller gains and limits are adjusted to base values.

At 508, method 500 sets the SOOT_MAX_LATCH variable to a value of one toindicate that particulate filter regeneration is desired. Setting thevariable to a value of one indicates that particulate filterregeneration is desired. Additionally, in some examples, method 500 maybegin monitoring a section of road for road conditions such as presentroad grade and road grade a predetermined distance from the vehicle. Ifa road grade at the predetermined distance from the present road gradechanges by more than a threshold amount, method 500 may begin retardingspark if particulate filter temperature is less than a thresholdtemperature. By retarding spark timing before the road grade changes, itmay be possible to elevate particulate filter temperature to atemperature desirable for particulate matter regeneration before thevehicle enters a deceleration fuel shut-off mode. The present road gradeand road grade a predetermined distance from the vehicle's presentposition may be supplied via maps stored in the controller and the GPSsystem. In this way, conditions where the particulate filter may beregenerated may be anticipated so that the particulate filter isprepared for regeneration. Method 500 proceeds to 510 after the variableis set to a value of one.

At 510, method 500 judges if GPF temperature is greater than a thresholdtemperature. The GPF temperature may be measured or inferred from sparktiming and engine speed and load. If method 500 judges that GPFtemperature is greater than the threshold temperature, the answer is yesand method 500 proceeds to 512. Otherwise, the answer is no and method500 proceeds to 506. In one example, the threshold temperature is atemperature where soot stored combusts when exposed to air.

Further, in some examples, additional conditions may be evaluated at510. For example, if the vehicle is in cruise control mode and thevehicle is following a vehicle less than a threshold distance away,method 500 may proceed to 506 and 507 to operate the vehicle with speedcontroller gains adjusted to base gains so that speed may be controlledcloser to a desired speed in an effort to maintain a desired distance tothe vehicle being followed. However, if the vehicle is in cruise controlmode and the vehicle is following the vehicle at greater than thethreshold distance, method 500 may proceed to 512 in order to increasethe probability of entering deceleration fuel shut-off.

In some examples, the controller gains may be adjusted differentlydepending on whether the vehicle is in an adaptive cruise control modein which the vehicle is maintaining a distance behind a forward vehicleand controlling vehicle speed automatically, and further optionallydepending on whether the vehicle is in a lane-keeping mode wheresteering is carried out automatically based on detected road lanes. Forexample, as described below in 512, the routine may modify thecontroller gains and threshold limits based on the soot load, andfurther based on the type of vehicle speed control mode present.

At 512, method 500 modifies vehicle speed controller gains and limits tovalues that increase the possibility of entering deceleration fuelshut-off mode while the vehicle is in speed or cruise control mode. Thevehicle speed controller gains and limits may be adjusted to allowlarger variation in vehicle speed from the desired vehicle speed andmore rapid reductions in engine torque when vehicle speed is within adesired speed range (e.g., the desired speed range may extend from thevehicle speed lower limit to the vehicle speed upper limit). In oneexample, the controller values when the amount of soot stored in theparticulate filter is greater than a first threshold may expand thevehicle speed upper and lower limits further from the desired vehiclespeed than the vehicle speed upper and lower limits when the particulatefilter is not storing more than a first threshold amount of soot. Forexample, an upper speed limit when the amount of soot stored in theparticulate filter is greater than the first threshold may be 107 KPHwhen desired vehicle speed is 100 KPH and an upper speed limit when theparticulate filter is not storing more than a first threshold amount ofsoot may be 104 KPH when the desired vehicle speed is 100 KPH. A lowerspeed limit when the amount of soot stored in the particulate filter isgreater than the first threshold may be 93 KPH when desired vehiclespeed is 100 KPH and an lower speed limit when the particulate filter isnot storing more than a first threshold amount of soot may be 96 KPHwhen the desired vehicle speed is 100 KPH. Further, vehicle speedcontroller gains when an amount of soot stored in the particulate filteris greater than a first threshold may be increased as compared tovehicle speed controller gains when the amount of soot stored in theparticulate filter is less than the first threshold. For example aproportional vehicle speed controller gain when an amount of soot storedin the particulate filter is greater than the first threshold may be 2.On the other hand, the proportional vehicle speed controller gain whenan amount of soot stored in the particulate filter is not greater thanthe first threshold may be 1.2. Consequently, engine torque demands maychange quicker when the amount of soot stored in the particulate filteris greater than the first threshold so as to enter deceleration fuelshut-off more frequently (e.g., ceasing to fuel one or more enginecylinders while the engine is rotating). Method 500 proceeds to 514after vehicle speed controller gains and limits are adjusted.

Additionally, the gains and limits may be further adjusted based onwhether the vehicle is in an adaptive cruise control mode. If so, thegains and limits may be further adjusted. In one example, the amount ofincrease and/or decrease in the gains and/or limits (as a function ofsoot) may be decreased as the forward distance to the vehicle that isbeing followed decreases. In one example, the gains may approach thegains and limits used when soot is below the threshold as the distancedecreases to a minimum distance. In this way, as the following distancedecreases, tighter control of speed obtained. Likewise, the adjustmentto the gains based on soot may be decreased under conditions oflane-keeping control, as compared to manual steering control. Thus, evenwhen soot storage is above the threshold to trigger gain and limitadjustments, such adjustments are reduced or eliminated when inlane-keeping control mode and/or when the distance to a forward vehiclereaches a minimum threshold in an adaptive cruise control mode.

At 514, the vehicle is operated in speed or cruise control mode withlimits and gains that are based on the amount of soot stored in theparticulate filter exceeding a first threshold. The vehicle speed iscontrolled to a desired vehicle speed via adjusting one or more enginetorque actuators. Method 500 proceeds to 516 after beginning to operatethe vehicle with the revised vehicle speed controller parameters.

At 516, method 500 judges if vehicle conditions are acceptable to enterdeceleration fuel shut-off. In one example, method 500 may judge thatconditions are acceptable to enter deceleration fuel shut off when wheeltorque demand (e.g., a requested amount of torque requested via thevehicle speed controller) is less than a threshold wheel torque demand,when vehicle speed is greater than a threshold vehicle speed, and whenthe wheel torque demand has been less than the threshold wheel torquedemand for longer than a threshold amount of time. Such conditions mayresult from road conditions and operating in the speed control mode. Inother examples, method 500 may judge to enter deceleration fuel shut-offin response to a change in road grade or when a magnitude of a negativeroad grade is greater than a threshold. For example, if a GPS system orinclinometer indicates a change from a flat road grade, or a positiveroad grade to a negative road grade, method 500 may enter decelerationfuel shut-off. Further, if a magnitude of a negative road grade isgreater than a threshold, method 500 may enter deceleration fuelshut-off. The vehicle may enter a deceleration fuel shut-off mode whileoperating in cruise control or speed control mode. For example, if thevehicle begins traveling down a section of road with a negative gradethat allows vehicle speed to be maintained with a small wheel torquedemand, the vehicle may enter deceleration fuel shut-off mode. If method500 judges that conditions are acceptable for entering deceleration fuelshut-off, method 500 proceeds to 518. Otherwise, method 500 proceeds to506. Thus, deceleration fuel shut-off mode may not be entered if vehicleconditions arising from road conditions of a section of road the vehicleis traveling on are insufficient to lower the wheel torque demand for apredetermined amount of time while vehicle speed is greater than athreshold speed.

At 518, method 500 ceases to inject fuel to one or more engine cylindersand enter deceleration fuel shut-off mode. By ceasing to inject fuel toone or more cylinders, an excess amount of air may pass through theengine to the particulate filter facilitating combustion of soot storedin the particulate filter. Further, in some examples, the enginethrottle position may be adjusted based on the amount of soot stored inthe particulate filter. For example, if the amount of soot stored in theparticulate filter is greater than the first threshold amount, a firstamount of air may be allowed to flow through the engine to theparticulate filter. If the amount of soot stored in the particulatefilter is less than the first threshold amount, a second amount of airgreater than the first amount of air may be allowed to flow through theengine to the particulate filter. In this way, the combustion rate ofsoot in the particulate filter may be controlled. Method 500 proceeds to520 after the vehicle enters deceleration fuel shut-off mode.

At 520, method 500 judges if it is desirable to exit deceleration fuelshut-off (DFSO) mode. In one example, deceleration fuel shut-off modemay be exited in response to an increase in requested wheel torque.Deceleration fuel shut-off mode may also be exited if vehicle speed isreduced to less than a threshold speed. If method 500 judges to exitdeceleration fuel shut-off mode, the answer is yes and method 500proceeds to 522. Otherwise, the answer is no and method 500 returns to518.

At 522, method 500 judges if soot load or the amount of soot stored inthe particulate filter is less than (L.T.) a second thresholdGPF_LOAD_MIN. In one example, the amount of soot stored in theparticulate filter is based on a pressure change or drop across theparticulate filter. If method 500 judges that the amount of soot storedin the particulate filter is less than the second threshold, the answeris yes and method 500 proceeds to 524. Otherwise, the answer is no andmethod 500 proceeds to 506.

At 524, method 500 clears the variable SOOT_MAX_LATCH by setting it to avalue of zero. Resetting the variable indicates that particulate filterregeneration is complete. Method 500 proceeds to 506 afterSOOT_MAX_LATCH is cleared.

Thus, the method of FIG. 5 provides for a method for regenerating aparticulate filter, comprising: operating a vehicle in an automaticspeed control mode; adjusting one or more vehicle speed control modeparameters in response to an amount of soot stored in a particulatefilter exceeding a first threshold while operating the vehicle in theautomatic speed control mode; and entering a deceleration fuel shut-offmode while operating the vehicle in the automatic speed control mode.The method includes where torque of an engine is adjusted to maintainvehicle speed at a desired speed in the automatic speed control mode.The method also includes where adjusting one or more vehicle speedcontrol mode parameters increases a possibility of entering thedeceleration fuel shut-off mode. The method further comprises adjustingthe one or more vehicle speed control parameters in response to theamount of soot stored in the particulate filter being less than a secondthreshold amount. The method further comprises retarding spark timing inanticipation of a road condition and a temperature of the particulatefilter. The method includes where the road condition is a change in roadgrade.

Referring now to FIG. 6, an example vehicle operating sequence for avehicle operating in a cruise control mode on a road is shown. Verticalmarkers at times T0-T6 represent times of interest during the sequence.All of the plots occur at a same time and same vehicle operatingconditions. In cruise control mode, the vehicle wheel torque command ormotive power source torque demand is provided via a vehicle speedcontroller other than a driver. The vehicle speed controller hasobjectives in cruise control mode that influence the torque demandoutput by the controller, and the objectives may be at least partiallydefined by constraints such as maximum and minimum vehicle speed limits.The vehicle speed controller may vary an engine torque demand in cruisecontrol mode to hold vehicle speed within the desired vehicle speedrange without driver input to the vehicle speed controller or withoutthe driver requesting torque from the engine. Thus, the torque commandin cruise control mode may be based on a desired vehicle speed requestedby a driver. The vehicle speed controller may adjust torque of a motivetorque source to achieve the desired vehicle speed.

The first plot from the top of FIG. 6 is a plot of vehicle speed versustime. The horizontal axis represents time and time increases from theleft side of the plot to the right side of the plot.

The vertical axis represents vehicle speed and vehicle speed increasesin the direction of the vertical axis arrow. Horizontal line 602represents a maximum vehicle speed limit. Horizontal line 606 representsa minimum vehicle speed limit. Dash-dot line 604 represents a desiredvehicle speed. The desired vehicle speed may be selected by the driveror it may be based off of a speed limit of a road on which the vehicleis traveling. In one example, the maximum and minimum vehicle speedlimits 602 and 606 are based on the desired vehicle speed. For example,the maximum and minimum vehicle speeds may be the desired vehicle speedplus an offset (e.g., maximum vehicle speed) and minus the offset (e.g.,minimum vehicle speed) respectively. The actual vehicle speed isindicated by the solid line.

The second plot from the top of FIG. 6 is a plot of vehicle speedcontroller gain versus time. In one example, the gain is a proportionalgain; however, depending on the type of vehicle speed controller, thegain may be an integral gain or a matrix of gain values. In thisexample, the gain is a gain for a proportional controller. Thehorizontal axis represents time and time increases from the left side ofthe plot to the right side of the plot. The vertical axis representsvehicle speed controller gain and the vehicle speed controller gainincreases in the direction of the vertical axis arrow.

The third plot from the top of FIG. 6 is a plot of gasoline particulatefilter (GPF) soot load or the amount of soot stored in the particulatefilter versus time. The vertical axis represents an amount of sootstored in the particulate filter and the amount of soot increases in thedirection of the vertical axis arrow. The horizontal axis representstime and time increases from the left side of the plot to the right sideof the plot. Horizontal line 610 represents an upper or first thresholdsoot load above which vehicle speed controller control parameters may beadjusted. Horizontal line 612 represents a lower or second thresholdsoot load below which vehicle speed controller control parameters arebase values.

The fourth plot from the top of FIG. 6 is a plot of vehicle decelerationfuel shut-off mode (DFSO) state versus time. The horizontal axisrepresents time and time increases from the left side of the plot to theright side of the plot. The vertical axis represents DFSO state and DFSOis active when the trace is at a higher value near the vertical axisarrow. DFSO is not active when the trance is at a lower level near thehorizontal axis.

The fifth plot from the top of FIG. 6 is a plot of gasoline particulatefilter (GPF) regeneration state versus time. The horizontal axisrepresents time and time increases from the left side of the plot to theright side of the plot. The vertical axis represents GPF regenerationand the GPF is being regenerated when the trace is at a higher valuenear the vertical axis arrow. The GPF is not being regenerated when thetrance is at a lower level near the horizontal axis.

At time T0, the vehicle is in cruise control mode and the controllergain is at a lower level. The vehicle speed upper limit and the vehiclespeed lower limit are relatively close to the desired vehicle speed 604.The GPF soot load is less than 610 and the vehicle is not in DFSO mode.Further, the GPF is not being regenerated. These conditions may beobserved when the vehicle is traveling on a level road in cruise controlmode.

Between time T0 and time T1, the GPF soot load continues to increase andthe vehicle speed is maintained between upper limit 602 and lower limit606. The controller gain and vehicle speed limits remain at their samerespective levels and the vehicle does not enter DFSO or GPFregeneration.

At time T1, the GPF soot threshold exceeds the first threshold level610. The vehicle speed controller gain is increased and the vehiclespeed upper limit is increased and the vehicle speed lower limit isdecreased in response to the soot threshold. By changing the vehiclespeed controller gain and the vehicle upper speed limit and vehiclelower speed limit, engine torque reductions may increase in magnitudeand duration so that DFSO and GPF regeneration may occur more frequentlyand for longer durations. In one example, tables in memory containempirically determined vehicle speed controller gains and vehicle speedlimit adjustments that are a function of the amount of soot stored inthe particulate filter. The vehicle does not enter DFSO and the GPF isnot being regenerated.

At time T2, the vehicle enters DFSO mode and passive GPF regenerationbegins. By allowing air to flow through engine cylinders as the enginerotates after fuel is shut off to the cylinders, combustion of soot inthe particulate filter may be initiated. The amount of soot stored inthe particulate filter begins to be reduced upon GPF regenerationbeginning. The vehicle is decelerating while in DFSO mode. The adjustedvehicle speed controller gain and vehicle speed limits may provide forlarger and more rapid changes in engine torque so that DFSO mode may beentered sooner and for a longer duration as compared to if the vehiclespeed controller operated with base control parameters.

At time T3, the vehicle speed approaches the lower vehicle speed limit606 and engine torque is increased (not shown) so that vehicle speedremains between upper vehicle speed limit 602 and lower vehicle speedlimit 606. The vehicle exits DFSO mode and GPF regeneration mode inresponse to the engine torque increase. The amount of soot stored in theGPF remains above second threshold 612 so the vehicle speed controllergain and vehicle speed limits remain at their same levels.

At time T4, the vehicle enters DFSO again and GPF regeneration beginsfor a second time. The vehicle enters DFSO as the vehicle decelerates.The amount of soot stored in the particulate filter is reduced as theparticulate filter regenerates via combusting soot stored in theparticulate filter using air pumped through the engine. The vehiclespeed controller gain and vehicle upper and lower speed limits remain attheir previous levels.

Between time T4 and time T5, the amount of soot stored in theparticulate filter continues to decrease. All other operating conditionsremain at their respective levels.

At time T5, the amount of soot stored in the particulate filter isreduced to less than threshold 612. The vehicle exits DFSO and GPFregeneration in response to the amount of soot stored in the particulatefilter being less than threshold 612. The upper vehicle speed limit isreduced and the lower vehicle speed limit is increased in response tothe amount of soot stored in the particulate filter being less thanthreshold 612. Further, the vehicle speed controller gain is reduced inresponse to the amount of soot stored in the particulate filter beingless than threshold 612.

Between time T5 and time T6, the amount of soot stored in theparticulate filter remains less than the first threshold level 610.Therefore, the vehicle speed controller gain and vehicle speed upper andlower limits remain at their respective base levels where the vehicle isexpected to enter deceleration fuel shut-off less frequently and forshorter durations. The vehicle does not enter deceleration fuelshut-off, nor is the particulate filter regenerated.

At time T6, the vehicle enters deceleration fuel shut-off mode, but theparticulate filter is not regenerated because particulate filtertemperature (not shown) is not high enough to regenerate the particulatefilter. The vehicle enters deceleration fuel shut-off for only a shortduration and then exits. The vehicle speed controller gain and vehiclespeed upper and lower limits remain at their respective base levelssince the amount of soot stored in the particulate filter is less thanthe first threshold level 610.

In this way, the gasoline particulate filter may be periodicallyregenerated via adjusting vehicle speed controller control parameters sothat the vehicle may enter deceleration fuel shut-off mode morefrequently where the particulate filter may be regenerated. In addition,the vehicle may remain in vehicle speed control mode so that the vehiclemay continue to operate in an expected way.

Note that the example control and estimation routines included hereincan be used with various engine and/or vehicle system configurations.Further, the methods described herein may be a combination of actionstaken by a controller in the physical world and instructions within thecontroller. The control methods and routines disclosed herein may bestored as executable instructions in non-transitory memory and may becarried out by the control system including the controller incombination with the various sensors, actuators, and other enginehardware. The specific routines described herein may represent one ormore of any number of processing strategies such as event-driven,interrupt-driven, multi-tasking, multi-threading, and the like. As such,various actions, operations, and/or functions illustrated may beperformed in the sequence illustrated, in parallel, or in some casesomitted. Likewise, the order of processing is not necessarily requiredto achieve the features and advantages of the example embodimentsdescribed herein, but is provided for ease of illustration anddescription. One or more of the illustrated actions, operations and/orfunctions may be repeatedly performed depending on the particularstrategy being used. Further, the described actions, operations and/orfunctions may graphically represent code to be programmed intonon-transitory memory of the computer readable storage medium in theengine control system, where the described actions are carried out byexecuting the instructions in a system including the various enginehardware components in combination with the electronic controller. Thecontrol actions may also transform the operating state of one or moresensors or actuators in the physical world when the described actionsare carried out by executing the instructions in a system including thevarious engine hardware components in combination with one or morecontrollers.

This concludes the description. The reading of it by those skilled inthe art would bring to mind many alterations and modifications withoutdeparting from the spirit and the scope of the description. For example,I3, I4, I5, V6, V8, V10, and V12 engines operating in natural gas,gasoline, diesel, or alternative fuel configurations could use thepresent description to advantage. The following claims particularlypoint out certain combinations and sub-combinations regarded as noveland non-obvious. These claims may refer to “an” element or “a first”element or the equivalent thereof. Such claims should be understood toinclude incorporation of one or more such elements, neither requiringnor excluding two or more such elements. Other combinations andsub-combinations of the disclosed features, functions, elements, and/orproperties may be claimed through amendment of the present claims orthrough presentation of new claims in this or a related application.Such claims, whether broader, narrower, equal, or different in scope tothe original claims, also are regarded as included within the subjectmatter of the present disclosure.

1. A vehicle system, comprising: a spark ignited, direct injection, engine; an exhaust system coupled to the spark ignited engine, the exhaust system including a particulate filter; and a controller, the controller including executable instructions stored in non-transitory memory to operate the spark ignited engine and adjust a vehicle speed range about a desired vehicle speed between which vehicle speed is maintained by a vehicle speed control the range adjusted in response to an amount of soot stored in the particulate filter greater than a threshold amount.
 2. The vehicle system of claim 1, wherein the range is increased in response to the amount of soot stored in the particulate filter greater than the threshold amount.
 3. The vehicle system of claim 1, wherein the range is increased even when the desired vehicle speed is maintained fixed.
 4. The vehicle system of claim 3, further comprising additional instructions to, after having been increased, decrease the range in response to the amount of soot stored in the particulate filter below a lower threshold amount.
 5. The vehicle system of claim 4, further comprising additional instructions to control an amount of air flowing through the spark ignited engine during a condition of deceleration fuel shutoff in response to the amount of soot stored in the particulate filter.
 6. The vehicle system of claim 1, further comprising additional instructions to retard spark timing of the spark ignited engine in response to being within a threshold distance of an expected road condition where deceleration fuel shut off is expected.
 7. The vehicle system of claim 1, where the vehicle speed control includes a controller gain variable.
 8. The vehicle system of claim 7, where the range is defined by an upper limit and a lower limit.
 9. The vehicle system of claim 1, where the range is adjusted to increase a frequency of entering a deceleration fuel shut-off mode of operation.
 10. The vehicle system of claim 9, where fuel supplied to one or more engine cylinders ceases to flow in the deceleration fuel shut-off mode of operation.
 11. The vehicle system of claim 10, wherein the deceleration fuel shut-off mode causes particulate filter regeneration.
 12. The vehicle system of claim 1, further comprising additional instructions to cease fuel supplied to each engine cylinder in response to a particulate filter regeneration request.
 13. The vehicle system of claim 12, further comprising additional instructions to cease fuel supplied to each engine cylinder without a particulate filter regeneration request.
 14. The vehicle system of claim 12, further comprising additional instructions to cease fuel supplied to each engine cylinder without a particulate filter regeneration request during automatic vehicle speed control operation.
 15. A method for regenerating a particulate filter, comprising: operating a vehicle in an automatic speed control mode to maintain vehicle speed within limits about a desired vehicle speed; adjusting the vehicle speed control limits to increase a vehicle speed range about the desired vehicle speed in response to an amount of soot stored in a particulate filter exceeding a first threshold while operating the vehicle in the automatic speed control mode; and entering a deceleration fuel shut-off mode while operating the vehicle in the automatic speed control mode.
 16. The method of claim 15, where torque of an engine is adjusted to maintain vehicle speed at the desired speed in the automatic speed control mode.
 17. The method of claim 15, where the vehicle speed control mode limits is adjusted to increase a frequency of entering the deceleration fuel shut-off mode.
 18. The method of claim 15, further comprising adjusting the vehicle speed control limits in response to the amount of soot stored in the particulate filter being less than a second threshold amount.
 19. The method of claim 15, further comprising retarding spark timing in anticipation of a road condition and a temperature of the particulate filter.
 20. The method of claim 19, where the road condition is a change in road grade. 